Washington: With a new poll showing President Barack Obama getting a six point advantage over Mitt Romney after last week's Democratic National Convention, the Republican challenger has gone aggressive with his attacks on his opponent.

The new CNN/ORC poll released on Monday showed that Obama received a four point "bounce" from last week's Democratic convention, giving him a 52 percent-46 percent advantage over the former Massachusetts governor.

After the Republican National Convention in late August, the same poll showed the candidates at 48 percent each.

The sampling error means both results were statistically even, but the trend from the CNN survey and another one by Gallup showed Obama "did gain strength from his convention, principally by energizing the Democratic base", CNN polling director Keating Holland said.

The Gallup daily tracking poll released on Sunday showed Obama opening up his largest margin over Romney since early July - 49 percent to 44 percent - which also was statistically even due to the margin of error.

It was conducted Sep 2-8, a time window that included the entirety of the Democratic convention as well as a disappointing August jobs report that came out Friday. A week earlier, the same Gallup poll showed Obama with a 47 percent-46 percent advantage after the Republican convention.

Romney campaign pollster Neil Newhouse advised against anyone getting "too worked up about latest polling"."While some voters will feel a bit of a sugar-high from the conventions, the basic structure of the race has not changed significantly," Newhouse wrote in the memo made public Monday.

In more bad news for Romney, Obama's campaign announced Sunday it raised $114 million in August, topping the challenger's monthly haul for the first time since April.

Meanwhile, attacking Obama in the vital battleground state of Ohio, Romney accused the president of moving the country toward a debt-laden, big government society similar to failing European nations like Greece.

"He wants to fundamentally transform America," he said, suggesting that instead of "forward", "forewarned" would be more appropriate as Obama's campaign slogan.